Anti-chatter switch



y 1953 H. E. CORBITT 2,835,762

ANTI-CHATTER SWITCH Filed March 28. 1955 YIIIIIIIIIII. m\\\\\\\\\\ 2b 3 FIG. 4

IN V EN TOR. HOWARD E. CORE/T7 A TTORN Y United States PatentG ANTI-CHATTER swrrcn Howard E. Corbitt, Monrovia, Califi, assignor to Aeroietgfiriieral Corporation, Azusa, Calif., a corporation of Application March 28, 1955, Serial No. 497,050

Claims. (Cl. 200-88) This invention relates to electric relays and more particularly to electric relays of the thermal type, and has for its object to provide such a relay which will be free of contact chatter or flutter.

A thermal relay is a type which operates by the eifect of heat. metal provided with contacts which are adapted to open and close in accordance with the heat. The heating effeet is commonly produced by a heater coil associated with a bi-metal strip so that as heat is developed by the coil the strip bends to move its contact in relation to the other'contact. In this way the contacts are opened and closed in accordance with the heat.

It is a characteristic of this type of relay that the motion of the bi-metallic leaf or strip is inherently slow; and in consequence, it often happens that the make or break of the contacts is not sharp or distinct. Thus, there is a tendency to chatter as the contacts first move together or away from each other, as the case may be. Such chatter is undesirable as it causes contact deterioration which can result in circuit failure, mechanical locking, or snagging. Furthermore, high voltage transients may sometimes result, causing insulation puncture; or they may otherwise affect circuit operation adversely. Moreover, the contacts of a thermal relay are often used to actuate devices in adjacent circuits and in consequence such chatter is likely to cause abnormal operations in these affected circuits.

In accordance with the present invention the undesirable chatter is greatly reduced or eliminated by the addition of a coil, herein called an anti-chatter coil, associated with the contact leaves or strips. As the contact leaves themselves normally comprise magnetic material, current flowing through the anti-chatter coil develops north and south poles in the strips. Since both strips are included in the magnetic circuit, the north poles of the two strips will be adjacent to each other and likewise the south poles of the two strips will be adjacent. Since like poles repel, this will produce a tendency of the contacts to remain apart so long as this magnetic field is applied.

A feature of the arrangement resides in the connection of the anti-chatter coil with the heater coil so that when the relay contacts are closed the heater coil and antichatter coil are de-energized simultaneously. By this arrangement, the repelling magnetic force is removed at the moment of contact so that the contacts press tightly together, resulting in no chatter. The converse occurs as the heater cools, so that in cooling the contact breaks suddenly.

Further features reside in the arrangement of the antichatter coil in relation to the contact strips.

A related feature resides in an arrangement whereby the thermal relay contacts are normally closed and are caused to open positively when a heater coil and a magstood from the following detailed description and the acompanying drawings, of which:

It normally consists of a strip or strips of bi-,

Fig. 1 is a cross-section view taken at line 1-1 of Fig. 2 showing a thermal relay in accordance with this invention;

Fig. 1a shows in cross-section a detail of a bi-metal strip used in the construction of Fig. 1;

Fig. lb shows a detail of the strips in relation to an anti-chatter coil as used in Fig. 1;

Fig. 2 is an end view of the relay of Fig. 1;

Fig. 2a is an elevation view and Fig. 2b a cross-section view taken at line 2b-2b of Fig. 2a;

. Fig. 3 shows a circuit in which the thermal relay of Figs. 1 and 2 may be used; and

Fig. 4 shows another circuit in which the thermal relay of Figs. 1 and 2 may be used.

Referring to the drawings Figs. 1 and 2 show a thermal-relay construction comprising a pair of strips 1 and 2 interleaved and supported between insulating pieces 3, 4

and 5. Other insulating pieces 6 and 7 are shown interleaved between conductive strips 8 and 9, although members 6, 7, 8, and 9 may be omitted. This stack of insulating and conductive strips is mounted on a suitable "base'10 and clamped together by means (not shown).

The strips 1 and 2 protrude from the stack, and on the end of these strips are respective contacts 11 and 12. At least one of the strips, for example strip 2, is of a bi-metallic construction, a portion of which is shown in enlarged detail in Fig. 10 as being composed of two metallic members 2a and 2b of diiferent metals to create the bi-metallic character. As the selection of metals and the construction of such bi-metallic strips are well known, no further description is needed here. Preferably, both strips 1 and 2 are of the bi-metallic construction, so that the positions of the two strips are independent of ambient temperatures.

The bi-metallic strip 2 has wound around it a coil 13, which is the heater coil through which the current is sent to operate the relay. In accordance with the usual action of such a relay, when current flows through coil 13 the heat thereby created is imparted to the bi-metallic strip,

and expands the two metal portions 2a and 2b at different rates, thereby causing the strip to curl. The direction of curl when heated can be either that which causes contact 12 to move toward contact 11, or else it can be that which causes contact 12 to move away from contact 11. When sufiicient heat is developed contact 12 will touch contact 11 (when the bimetal arrangement is that which brings the contacts together) and will thereby close such circuit as is connected to the terminal ends of strips 1 and 2.

Since movement of strip 2 is rather slow and gradual with increased heat from the coil 13, there will come a time when contact 12 will just touch contact 11. At this point, there will be an imperfect contact resulting in chattering of the contacts.

To avoid this chattering effect in accordance with the present invention there is applied around both strips 1 and 2 a coil 14 which is herein referred to as an antichatter coil. The effect of coil 14 when current flows through it is illustrated in Fig. 1b, which shows parts of the strips 1 and 2. The magnetic field due to the current flow is as shown by the elipses and in the direc tion of the arrows for a given current direction. This will create the two adjacent north poles on the respective strips 1 and 2 and the two adjacent south poles on the same two strips. In consequence, the presence of these like poles opposite each other tends to hold the strips 1 and 2 apart. Heating of the heater coil however overcomes this tendency for the strips to be held apart so that the contacts 11 and 12 actually do come into contact (when the bi-metal is arranged in the direction to bring the strips towardeach other). When the relay is connected into a suitable circuit, the anti-chatter coil will be de-energized at this instant of contact so tha t the tion which has the advantage that the force between the H two contacts is approximately constant over a large range of voltage.

stead of being Wound around the two strips 1 and 2 is wound around a core 26 of magnetic material supported between a pair of yokes or end pieces 27, 28, of magnetic material. Each of the members 27 and 28 comprises a leg 29 to which the core member 26 attaches, and a large depending portion 30 provided with an opening 31 through which the strips 1 and 2 extend. Thus, the magnetic circuit of core 14 comprises the Nos. 26, 27, 28 and the magnetic strips 1 and 2, with only the rather small air gap between the strips 1 and 2 and the sides of the opening 31 of Nos. 27 and 28.

The arrangement of Figs. 2a and 2b is used in conjunction with the core 13 on leg 2 as shown, and this assembly will be incorporated into the structure of Fig. l.

A circuit utilizing the arrangement of this invention is shown in Fig. 3 which shows an application of the thermal relay to a simple cycling system in which the cycle occurs at a timed rate.

The contacts. 11 and 12 of the thermal relay of Fig. l are connected in series with coil 1.5 of another relay whose relay contacts 16 and 17 are in series with the parallel connected heater coil 13 and anti-chatter coil 14 of the thermal relay. The series elements 12, 11 and 15 are connected in parallel with the series circuit which include contacts 16 and 17; and D. C. voltage is applied at'terminals 18 and 19. When contacts 16 and 17 of the relay coil 15 are closed, the coils 13 and 14 are energized, which will close the thermal relay contacts 11 and 12. As these latter contacts close, coil 15 is energized which will open contacts 16 and 17 to deenergize the heater coil 13. 7 As the heater cools, its thermal contacts 11, 12 will open, which in turn will deenergize the relay coil 15. This causes the contacts 16 and 17 again to ClOSe and the cycle repeats. The timing of the opening and closing of the contacts depends on the rate of heat transfer at the heater.

In Figs. 2a and 2b the coil 14, in-

force due to the anti-chatter coil is applied when thermal relay contacts 11 and 12 open. Since this force is applied in such a manner as to further open the contacts, chatter does not occur. As the thermal relay cools and contacts 11, 12 close, this force is removed causing the contacts to press tightly together and preventing chatter.

It will be recognized that there will be many other applications to which the thermal relay may be put. It will further be recognized that variations may be made in the construction of the thermal relay without departing from the invention and such variations may occur to those skilled in the art.

Although the preferred embodiments of the invention have been illustrated and described as comprising two Fig. 4 is a schematic diagram showing how the antichatter device maybe applied to a normally closed thermal relay. In this case, the relay of Fig. 1 is considered normally to have its contacts 11 and 12 in contact with each other when the heater coil is not energized; and the relationship of the metals of the 'bi-metal strip 2 is such that when heat is applied the strip 2 curls away from strip 1, to open the contacts. In Fig. 4, the heater coil 13 is connected in parallel with a relay coil 25 having two sets of contacts, 21, 22 and 23', 24 the contacts 21, 22 being closed when coil 25 is energized and the contacts 23, 24 being closed when the coil 25- is (re-energized. Elements 25 and 13 are connected across the voltage source at 18, 19, in series with contacts 11, 12 of the thermal relay the anti-chatter coil 14 of which is. in series with contacts 23, 24 and across. the voltage source. A load 21) is in series with contacts 21, 22 across thevoltage source.

Thermal relay contacts 11 and 12 are normally closed so that current is normally flowing through elements 13 and 25 from the D. C. source connected at terminals 18 and 19.

Energization of coil 25 closes contacts 21, 22 which energizes the load and rte-energizes anti-chatter coil 14 The.

strips each of which contains one of the contacts, it may be possible under some conditions to use only one flexible strip in which case there will be one contact on that strip; and the opposite contact will be on another mounting. For example, the element 1 of Fig. 1 need not necessarily be a flexible strip; this particular element could for example be rigid. In such case the strip vhich is flexible may be made to flex under changes of the magnetic-field. Such flexure may be sufiicient to make or break the contacts as already described.

The invention is not limited to the particular embodiments disclosed and described which are given by way of illustration rather than of limitation; and it should be understood that the invention is not limited except in accordance with the scope of the appended claims.

I claim:

1. A thermal relay comprising a pair of strips of magnetic material, at least one of said strips being a bi-metal strip whereby the application of heat to it causes it to curl in one direction, a heater coil related to said bi-metal strip, a pair of contacts on said strips and an anti-chatter coil wound around both said strips whereby current through said anti-chatter coil produces like poles opposite to each other on the two strips to tend to keep them separated, and means disconnecting the anti-chatter coil when the contacts are made to just touch by energization by said. heater coil.

2. A thermal relay comprising a pair of strips of magnetic material, at least one of said strips being a bimetal strip whereby the application of heat to it causes it to curl in one direction, and to curl in the opposite direction when its temperature falls, a heater coil related to said bi-metal strip, a pair of contacts on said strips and an antichatter coil related to said strips, whereby current through said anti-chatter coil produces like poles opposite to each other on the two strips to tend to keep them separated, and means disconnecting the anti-chatter coil when the contacts are made to just touch by energization by said heater coil.

3. A thermal relay comprising a strip of magnetic material said strip being a bi-metal strip whereby the application of heat to it causes it to curl in one direction and a fall in temperature causes it to curl in the opposite direction, a heater coil related to said strip, a contact onsaid strip, a second contact in proximity to the firstmeniioned strip whereby said contacts make or break in dependence on the. temperature of said strip, and an antichatter coil. having a magnetic field, said strip being located. in said magnetic field, so that current through said antiechatter coil produces a tendency of said strip to move in said magnetic field in the direction tending to separate said contacts, and means disconnecting the antichatter coil when the contacts are made to just touch by energization-v by said heater coil, whereby said contacts press more tightly against each other.

4. A thermal relay comprising. a strip of magnetic material, said strip being. a bi-metal strip whereby the application of heat to it causes it to curl in one direction .anda drop. of. temperatures causes it to curl in the opposite direction, a heater coilrelated to said strip, a contact on said strip, a second contact in proximitytothe first mentioned contact, and an anti-chatter coil having a magnetic field, said strip being located in said magnetic field so that current through said anti-chatter coil produces a tendency of said strip to move in said magnetic field and thereby tends to cause said contacts to move relatively to each other. and means altering the energization of the anti-chatter coii when the contacts are made or broken.

5. A thermal relay comprising pair of strips of magnetic mate! at least one of said strips being a bimetai strip whereby ifl-f; application of heat to it causes it to curl in one direction, a heater coil related to said bi-metal strip, a contact on each of said strips, said contacts being opposed to each other whereby they are made or broken in dependence on the relative movement of said strips, a magnetic circuit including said strips, an

anti-chatter coil magnetically related to said magnetic circuit, whereby current through said anti-chatter coil produces like poles opposite to each other on the strips to tend to keep them separated, and means disconnecting the anti-chatter coil When the contacts are made to just touch by energization by said heater coil.

References Cited in the file of this patent UNITED STATES PATENTS 1,867,380 Runyon July 12, 1932 2,863,638 Noths'tine June 4, 1935 2,611,656 Jackel Sept. 16, 1952 2,764,647 Leslie et al. Sept. 25, 1956 FOREIGN PATENTS 135,006 Australia Nov. 2, 1949 

